We all have the “dots” on our iPhone to show the signal strength, but is that enough? I would prefer something a little more granular than that on my iPhone. Fortunately there is an easy way of altering the signal strength display to do just that, You don’t have to jailbreak your iPhone and the change is reversible.
To do this you need to access the hidden “Field Test Mode” on your iPhone. That can be done by entering *3001#12345#* on the iPhone keypad, then tapping the Call button. This will replace the display of the signal strength at the top left of the iPhone screen using the standard “dots” (left figure below) and with a numerical signal strength readout (right figure below). The value will be in decibels (dBm) ranging from -40 to -130, with -40 being the strongest possible signal and -130 being no signal at all.
This number represents the Received Signal Strength Indication (RSSI) – a measure of the power present in the received radio signal. Interpreting the RSSI value:
- -40 dBm to -60 dBm – very strong signal
- -61 dBm to -95 dBm – strong signal
- -96 dBm to -110 dBm – satisfactory signal
- -111 dBm or less – poor signal
Hitting the Home button will exit Field Test Mode and return your iPhone to the normal signal strength display.
Now the process discussed thus far only displays the signal strength while Field Test Mode is invoked. I prefer to have the signal strength displayed all the time in decibels (dBm). To accomplish this dial *3001#12345#* on the iPhone keypad again. Instead of leaving Field Test Mode using the Home button, hold down the power/sleep button until is shows the “Slide to power off” message, then hold down the iPhone Home button. This will “force quit” the Field Test App. Now the signal strength is left displaying in decibels. If you tap on the displayed value, it will toggle between displaying the signal strength in dBm and the original “dots”.
To return the phone to the original signal strength display, repeat the process. This will work with an iPhone running iOS 4.1 or later.
I modified my iPhone 5 several months ago and prefer this more granular report on the signal strength. I should note too that the change persists across updates. I recently updated to iOS 9 and the change is still in place.
See my other iOS articles